Una megaciutat és definida com una àrea metropolitana amb més de 10 milions d’habitants. Algunes definicions requereixen que tingui una densitat demogràfica mínima de 2000 persones/km. Pot estar formada per una, dos o més àrees metropolitanes que s’han unit físicament. Els termes de conurbació i metroplex s’apliquen també als casos de varies àrees urbanes unides.

The megacity state: The world’s biggest cities shaping our future

Allianz Risk Pulse, 2015

November 30, 2030, late autumn morning: Who hasn’t wondered how life will be in the future. Imagine you live in a modern megalopolis, with millions of other people? What would have changed from today? Often it is the small, mundane things that ultimately make the biggest difference. Let’s fast-forward to the year 2030. Whereas, in the past, after getting up you may have only checked e-mails and posts on your smartphone, now you also take a quick glance at a wall monitor. It tells you: Apartment battery 80% charged. The solar panels and algae bioreactors that cover your tower block are working well. There is plenty of water too, captured during last night’s rainstorm. You notice the view has improved since the green roof law came in. Which reminds you: the vegetables in the highrise across the road are ready to collect. Gone are the days when fruit and vegetables were grown only in the countryside – now, crop fields stretch over several stories in so-called vertical farms.

It is a beautiful sunny morning. However, air pollution is particularly high on days like this so the smart traffic management system has restricted private vehicles. No matter, cycling to the station is good exercise. Before you set off, you empty your garbage: food waste into the composting tube, the rest into the tube for the district power plant.

Outside, you cycle past the driverless cars reserved for senior citizens – these days 15% of the world’s population is older than 60. On your way to the next local transport stop, you take a route that is lined in its entirety by solar panels. You then pass a construction site where entire apartment blocks are created using 3D printers. When you reach the railway station, you decide to take the express bus. Although the magnetic levitation train you initially wanted to take is even faster, it is totally packed today. While the bus is racing past endless traffic jams, you relax into your seat to prepare for the day ahead in the megacity.

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Energy and material flows of megacities

C.A. Kennedya, I. Stewarta, A. Facchinib, I. Cersosimob, R. Meleb, B. Chenc, M. Udaa, A. Kansald, A. Chiue, K. Kimf, C. Dubeuxg, E. L. La Rovereg, B. Cunhag, S. Pincetlh, J. Keirsteadi, S. Barlesj, S. Pusakak, J. Gunawank, M. Adegbilel, M. Nazariham, S. Hoquen, P. J. Marcotullioo, F. G. Otharánp, T. Genenaq, N. Ibrahima, R. Farooquir, G. Cervantess, and A. D. Sahint (PNAS), 2015

Understanding the drivers of energy and material flows of cities is important for addressing global environmental challenges. Accessing, sharing, and managing energy and material resources is particularly critical for megacities, which face enormous social stresses because of their sheer size and complexity. Here we quantify the energy and material flows through the world’s 27 megacities with populations greater than 10 million people as of 2010. Collectively the resource flows through megacities are largely consistent with scaling laws established in the emerging science of cities. Correlations are established for electricity consumption, heating and industrial fuel use, ground transportation energy use, water consumption, waste generation, and steel production in terms of heating-degree-days, urban form, economic activity, and population growth. The results help identify megacities exhibiting high and low levels of consumption and those making efficient use of resources. The correlation between per capita electricity use and urbanized area per capita is shown to be a consequence of gross building floor area per capita, which is found to increase for lower-density cities. Many of the megacities are growing rapidly in population but are growing even faster in terms of gross domestic product (GDP) and energy use. In the decade from 2001–2011, electricity use and ground transportation fuel use in megacities grew at approximately half the rate of GDP growth.

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The problem with megacities

Joel Kotkin, Chapman University (2014)

No phenomenon more reflects the sheer power and appeal of urbanism than the rise of megacities, which we define as an urban area with more than 10 million residents (defined as areas of continuous urban development). Until recent decades there were only three — Tokyo and New York, joined by a third, Mexico City, only in 1975. Now the megacity has become a global phenomenon that has dispersed around the planet. There were 29 such cities in 2014 and now account for roughly 13% of the world’s urban population and 7% of the world’s total population. Urban boosters such as Harvard’s Ed Glaeser suggest that megacities grow because “globalization” and “technological change have increased the returns to being smart.”  And to be sure, megacities such Jakarta, Kolkata (in India), Mumbai, Manila, Karachi, and Lagos — all among the top 25 most populous cities in the world — present a great opportunity for large corporate development firms who pledge to fix their problems with ultra-expensive hardware. They also provide thrilling features for journalists and a rich trove for academic researchers.

Like Mr. Glaeser, many Western pundits find much to celebrate about the megacities mushrooming in low-income countries. To them, the growth of megacities is justified because it offers something more than unremitting rural poverty. But surely there’s a better alternative than celebrating slums, as one prominent author did recently in Foreign Policy bizarrely entitled “In Praise of Slums”. As demonstrated in our new paper on global cities developed with the Civil Service College of Singapore, many of these emergent megacities in Africa and elsewhere in the developing world lack of an economic basis sufficient to substantially compete beyond their national or nearby regional markets. As a result, the rise of megacities in the developing world may be laying the foundation for an emerging crisis of urbanity, where people crowd into giant cities that lack of the economic and political infrastructure to improve their lives. At the end of this paper, we try to suggest that they may be better solutions that steer growth to smaller cities and towns, and even seek out ways to improve the life in rural villages.

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Analyzing urban systems: Have mega-cities become too large?

Klaus Desmet, Esteban Rossi-Hansberg, 2014

With the trend toward greater urbanization and the rapid emergence of mega-cities continuing unabated, many policy makers ask themselves whether some cities are becoming too large, and whether policies should be aimed at stimulating the growth of intermediate-sized cities. In this chapter we use a simple model of a system of cities, together with some basic urban and aggregate data, to answer some of the following questions. Would there be any welfare gains from reducing the size of mega-cities and increasing that of intermediate-sized cities? Is there any sense in implementing policies that make cities more equal in terms of efficiency and amenities? Should infrastructure investments be focused on improving life in the most lagging cities? Is it advisable for policy to have a small city bias? As developing countries continue to grow, will their largest cities tend to become even larger or are we likely to see a more equal spatial distribution of people? We provide quantitative answers to these questions by using data from the U.S., as well as from two large developing countries, China and Mexico.

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Megacities sustainable development and waste management in the 21st century

Antonis Mavropoulos, ISWA STC Chair, CEO EPEM SA

The purpose of this paper is to present the challenge of waste management for the emerging megacities of the developing world and transition countries and to outline major issues that have to be further elaborated in order to create sustainable patterns in waste management.

Megacities face tremendous environmental challenges and threats for human health. In this framework the role of waste management is becoming more and more crucial both for the daily life as well as for the long to medium term sustainability of megacities. The challenge of a successful waste management in megacities is one of the most demanding for public authorities and the waste management industry. This paper outlines some of the major characteristics of megacities that substantially affect waste management activities like their rapid growth, the symbiosis of wealth and poverty, the role informal economy, governmental and institutional issues and their role in the globalization process.

Then it focuses on how the characteristics of megacities create certain conditions and implications for waste management depending on the megacity growth profile. Special importance is given to the role of the informal sector and the experiences related its integration to waste management systems. While there is no certain way for a successful waste management approach, there are things that must be avoided and they are presented in a Failure Receipt. Also, some generic suggestions are made on how to increase the possibilities of a successful approach. Finally, it is proposed a view and certain questions that must be answered in order to understand how sustainable waste management can be created within the triangle megacities – globalization – waste management.

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